1. Technical Field
The present invention relates to a hydrogen generating apparatus, a method of manufacturing the hydrogen generating apparatus, and a fuel cell power generation system.
2. Description of the Related Art
A fuel cell is an apparatus that converts the chemical energies of fuel (hydrogen, LNG, LPG, methanol, etc.) and air directly into electricity and heat, by means of electrochemical reactions. In contrast to conventional power generation techniques, which employ the processes of burning fuel, generating vapor, driving turbines, and driving power generators, the utilization of fuel cells does not entail combustion processes or driving apparatus. As such, the fuel cell is the result of new technology for generating power that offers high efficiency and few environmental problems.
FIG. 1 is a diagram illustrating the operating principle of a fuel cell.
Referring to FIG. 1, a fuel cell 100 may include a fuel electrode 110 as an anode and an air electrode 130 as a cathode. The fuel electrode 110 receives molecular hydrogen (H2), which is dissociated into hydrogen ions (H+) and electrons (e−). The hydrogen ions move past an absorbent layer 120 towards the air electrode 130. This absorbent layer 120 corresponds to an electrolyte layer. The electrons move through an external circuit 140 to generate an electric current. The hydrogen ions and the electrons combine with the oxygen in the air at the air electrode 130 to generate water. The following Reaction Scheme 1 represents the chemical reactions described above.Fuel Electrode 110: H2→2H++2e−Air Electrode 130: ½O2+2H++2e−→H2OOverall Reaction: H2+½O2→H2O  [Reaction Scheme 1]
In short, the fuel cell can function as a battery, as the electrons dissociated from the fuel electrode 110 generate a current that passes through the external circuit. Such a fuel cell 100 is a pollution-free power source, because it does not produce any polluting emissions such as SOx, NOx, etc., and produces only little amounts of carbon dioxide. Also, the fuel cell may offer several other advantages, such as low noise and little vibration, etc.
In order for the fuel cell 100 to generate electrons at the fuel electrode 110, a hydrogen generating apparatus may be needed, which modifies a regular fuel containing hydrogen atoms into a gas having a high hydrogen content, as required by the fuel cell 100.
That is, examples of fuel cells being researched for application to portable electronic devices include the polymer electrolyte membrane fuel cell (PEMFC), which uses hydrogen as fuel, and the direct liquid fuel cell, such as the direct methanol fuel cell (DMFC), which uses liquid fuel directly. The PEMFC provides a high output density, but requires a separate apparatus for supplying hydrogen. Using a hydrogen storage tank, etc., for supplying the hydrogen can result in a large volume and can require special care in handling and keeping.
Because hydrogen exists as a gas at normal temperature, it has a very low storage efficiency. Using a pressurized tank for storing hydrogen may result in a very large volume for the fuel tank, whereas using an alloy for hydrogen storage may result in a very high mass. As such, the use of a hydrogen storage means may result in an increased size or mass of the overall fuel cell system, and thus may be difficult to utilize in portable electronic equipment.
In order for the fuel cell to suitably accommodate the demands in current portable electronic equipment (cell phones, laptops, etc.) for high-capacity power supply apparatus, the fuel cell needs to provide a small volume and high performance.
The fuel cell may employ a method of generating hydrogen after reforming fuel, such as methanol or formic acid, etc., approved by the ICAO (International Civil Aviation Organization) for boarding on airplanes, or may employ a method of using methanol, ethanol, or formic acid, etc., directly as the fuel.
However, the former case may require a high reforming temperature, and an external source of heat for initial operation. Since the reactions involved are endothermic, a continuous supply of heat may be required. Furthermore, this method may entail a complicated system, and high driving power, and is likely to have impurities (e.g. CO2, CO, etc.) included, besides pure hydrogen. On the other hand, the latter may entail the problem of very low power density, due to the low rate of a chemical reaction at the anode and the cross-over of hydrocarbons through the absorbent layer.
Another possible method may include reacting a metal with water to yield a metal oxide and hydrogen. However, since the reaction occurs only at the surfaces of the metal and the surfaces become coated with the metal oxide, the insides of the metal may remain unreacted, and only small amounts of hydrogen may be produced.
Moreover, the metal will react immediately upon contact with the water, to produce heat and terminate the reaction in a short duration of time. Therefore, in order for the fuel cell to continuously use this method, a flow type reactor may be required, which is able to initiate the reaction sequentially.
In the case of a reaction between water and metal powder, however, a batch type reactor may have to be employed instead of a flow type reactor. One reason for this is that the metal oxide formed as a product of the reaction between the water and metal powder may block the channel of the flow type reactor and thereby obstruct any further supply of reagents.
Therefore, an alternative may be to employ a batch type reactor, but this can entail difficulties in regulating the reaction rate, and can require additional equipment, such as a pump, for regulating the reaction rate.
As such, with a reformer that generates hydrogen by reacting a metal powder with water, it is difficult to control the rate at which hydrogen is generated, and the operation time of a system may become extremely short.